I don't really like showing of any pets; to me, it's not really about the pet, its more for the owners. It's hard to explain, but its like, dogs for example, would be far happier going for a run in the park. Cats don't want to be sitting in cages all day, really. As for guinea pigs, I've never been to a cavy show, but I imagine it would be very stressful for them; strange noises all around, strange people everywhere, etc. I could imagine a piggy getting very stresed out; why do it? It's not like the pets care if they get a fancy ribbon, or a certificate! They would much prefer a run on the floor, with toys.